Nanofiber is a relatively new and exciting technology that is disrupting industries all around the world!

These tiny strands of material are created using various techniques and methods that have been developed over the course of hundreds of years. Around the year 1600, a man named William Gilbert observed how fluid behaved when influenced by an electric field produced by rubbing a piece of amber. When the amber was brought close to the fluid, it created a shape now known as a Taylor cone (see Figure1). After this initial discovery, there were many scientists and academics who saw the potential of future applications. In 1887, British physicist Charles Vernon Boys published a manuscript on the development of nanofiber and how it could be produced in the future. Boys’ findings, along with many others, likely aided American inventor John Francis Cooley in filing the first modern electrospinning patent in 1900.  

taylor cone transitionzone resulting jet fluid
Figure 1: Taylor cone, transitionzone, and resulting jet of fluid.

The first attempt at spinning nanofibers was not attempted until 1934 by Anton Formhals.  He later published the first patent that provided a detailed description of the experimental procedure for producing nanofibers. This led to the first patent, filed by Harold Simons in 1966, for an actual machine that could produce nanofiber fabrics that were lightweight and thin on a larger scale.  Since then, nanofiber has become well known in the scientific community and is constantly being developed and improved upon. For more information on the history of nanofiber please click here. 

Nanofibers are usually about 50 to 500 nanometers in diameter, depending on the type of polymer used and the specifications of the design. In order to gain some perspective, check out Figure 1 to the right. The small speck is a piece of pollen. The large strand to the left is not a strand of nanofiber but a piece of human hair which is about 75,000 nm in diameter. If you look closely, you can see a network of nanofibers in the background. Now that’s tiny!

 

There is a wide variety of polymers and compounds that are used to create nanofibers such as polyurethane and lactic acid as well as naturally occurring polymers like collagen, cellulose, and gelatin. These polymers, as well as many others, are being used to improve and create a wide array of technologies including batteries, fuel cells, regenerative bio-tissue, and enhanced fluid filtration. Even though these fibers are almost impossible to detect with the naked eye, they are able to cover a tremendous amount of surface area relative to the overall volume of the material. This makes them perfect for filtering out unwanted particles that can slip through conventional filter fabric while remaining lightweight and breathable. 

nanofiber network comparison pollen particle human hair strand
Figure 2: Size comparison of a pollen particle to a strand of human hair. Nanofiber network in the background.

There are a few other reasons why having a fine fiber filtration layer is worth it. First, nanofiber filters have higher initial and ongoing efficiencies when compared to conventional filters. When clean, a network of nanofiber is able to capture dust and other harmful particles much better than clean filters that do not have a fine fiber layer. They are able to achieve these high levels of filtration using filtration methods such as interception, diffusion, and impaction. To learn more about filtration mechanisms, please click here

Another reason why nanofiber is superior is the fact that filters that use nanofiber layers last longer than other filters. Conventional filters reach the ends of their lives once the entire depth of the material has been loaded with debris. Nanofiber traps these particles on the surface and helps to prevent them from clogging up the other layers of material in the filter. Longer filter life means that the user will not have to buy filters as often. So, even though many fine fiber filters have higher up-front costs, they can help save a considerable amount of money in the long run. 

 

How is Nanofiber Made? 

Many different methods are used to create nanofibers such as template synthesis, melt-blowing, freeze-drying, and phase separation. The most commonly used technique is called electrospinning. Here at Filti, we spin our nanofiber from a base polymer. The process requires a high voltage electric field with positively and negatively charged ends, similar to a magnet. The polymer is loaded into an extruder at one end of the field and is quickly pulled out and stretched to the oppositely charged end, creating a long, thin strand. This results in an ultrafine network of nanofibers which is spun directly onto a base layer for backing and support. 

electrospinning and electrospraying
Figure 3: Electrospinning (top) and electrospraying (bottom)(source: https://www.frontiersin.org)
electrospinning process
Figure 4: Electrospinning (top) and electrospraying (bottom)(source: https://www.frontiersin.org)

Figure 4 above illustrates how the electrospinning process is carried out. The emulsion, loaded. As it exits the applicator, it immediately forms a Taylor cone as a result of the high voltage power supply creating an electric field between the applicator and the collector. As the fluid moves further into the field, it becomes more unstable and turns into a spiraling, flying jet. The jet of fluid then lands on a mat of material, non-woven in this case. The nanofiber network will then be used in conjunction with other layers of material or on its own for whatever the design specifications call for.

How Does Nanofiber Work?

When harmful particles such as dust, smoke, viruses, and bacteria encounter the nanofiber layer, it is almost as if they have entered a cursed forest from which few have ever escaped. As these particles attempt to navigate their way through the dense matrix, the seemingly endless array of fibers can easily intercept and prevent them from getting through by means of mechanical filtration as opposed to filters that use electrostatic filtration methods.  

A lot of the time you will hear mask manufacturers describe their products using efficiency and particle size. For example, N95 masks must meet a filtration efficiency of 95% down to 0.3 microns for them to pass certification. But why 0.3 microns? Anything larger than 0.3 microns is quite easy for filters to capture. For the smaller particles, the threshold between 0.1 and 0.3 microns is the toughest range of particles for filters to trap (see Figure 5). Once particles become smaller than 0.1 microns, they experience Brownian motion. 

This phenomenon occurs when particles are so small that when they run into gas molecules, they change course. Brownian motion bounces the particles so fast in such a short distance that it is almost guaranteed that they will run into the filter fibers.

Another way to think about it is that it acts as a fishing net. The web of continuous, overlapping fibers catches larger particles and prevents them from exiting out the other side. As more particles become trapped in the net, a sort of filter cake is formed throughout the material. This helps to improve the overall filtration efficiency of the media over time. 

typical hepa performance
Figure 5: Typical performance of a HEPA 99.97% filter.

Mechanical vs. Electrostatic Filtration

There are many intrinsic properties that set nanofiber apart from traditional filters. In addition to being cost-effective and easy to manufacture, nanofiber networks have high porosity and a large surface area-to-volume ratio. These properties make them extremely useful in applications such as protective clothing, energy storage, fiber optics, and organic tissue engineering. The main difference between nanofiber filters and other filters is the type of filtration method used. 

Many filters on the market today use electrostatic forces to attract and capture particles. This may sound cool at first, but they are often not as effective as other filtration media because they are less effective at trapping larger particles such as dust and mold. As they capture more dust and debris, they start to lose their static charge over time. As mentioned earlier, mechanical filters, such as our nanofiber material, tend to have higher initial efficiencies that do not rapidly decrease over time. This leads to longer filter life and cleaner air output. 

A Perfect Union

Here at Filti, all our products are manufactured using our patent-pending nanofiber technology but that does not mean they are not unique.  

dust layer on air filter

Some of our products, like our NF95 respirator, actually utilize two layers of nanofiber for increased filtration capabilities and effectiveness. Other products, like our Washable Home Furnace Filter, are constructed with coarser nanofiber strands for improved durability and tensile strength.

Regardless of design specifications, these nanofiber layers are the key to our high quality, mechanically efficient masks, filter media, and HVAC filters. All of our creations, not including the washable filters, target 95% efficiency for particles that are as small as 0.3 microns in diameter. This is equivalent to N95 certified mask capabilities and a MERV rating of 16. Our washable filters have a MERV rating of 13 due to the coarser fibers and larger pore spaces. To learn a little more about how filters are classified click here.

With the dawn of this new nanofiber technology, many are wondering, “Is nanofiber safe?” especially when it comes to breathing through it. The main concern is that pieces of the nanofiber network will break off and enter the lungs of the user. It is a common misconception that the material is made up of a lot of tiny, individual fibers when really, as discussed earlier, it is one continuous piece of polymer, like a really long strand of spaghetti that overlaps itself over and over again. If the material is cut, this may create more individual fibers, but they will still adhere to the layer of backing that they were initially spun onto so there is no need to worry about them flaking off. We also leech test our material before the final stages of production to ensure that no

nanofibers

Thanks for reading!

We are passionate about helping people stay healthy and improving the quality of the air that they are breathing. Our filter products are designed to help keep you and your family safe by filtering out the bad particles in the air.  Our mission is to make quality air filtration products available to all consumers and frontline workers.  For more information about Filti, our products, and our mission, visit our website at filti.com or send us an email at [email protected] We look forward to hearing from you!

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